This invention relates to a Karman's vortex street flow meter comprising a pair of conduits having a fluid to be measured introduced thereinto, and a detector for detecting the flow rate or flow speed of the measured fluid by detecting a frequency at which vortices of a Karman's vortex street are generated downstream of a junction where the measured fluid flowing through one of the conduits joins that flowing through the other conduit.
There have been already proposed a variety of types of the so-called Karman's vortex street flow meters comprising a conduit having a fluid to be measured flowing therethrough, a vortex generating rod immersed in the fluid flowing through the conduit perpendicularly to the direction of flow of the fluid to generate a Karman's vortex street downstream of the rod and a detector for detecting the frequency at which vortices of the Karman's vortex street are generated thereby to measure the flow rate or flow speed of the fluid.
Flow meters of the types referred to are disclosed and claimed, for example, in Japanese patent publication Nos. 1905/1969 and 9069/1981 and put to practical use as industrial measurement devices. There are also known a variety of types of a sucked air detector comprising the Karman's vortex street flow meter as described above utilized to detect the amount of air sucked into an associated internal combustion engine. Those sucked air detectors are disclosed and claimed, for example, in Japanese laid-open utility model application No. 5008/1975, Japanese laid-open patent application No. 130718/1976 and put to practical use. One of the conventional sucked air detectors has comprised a Karman's vortex street flow meter such as disclosed above, and an air cleaner disposed upstream of the Karman's vortex street flow meter to clean sucked air passed through an air introduction port. The sucked air introduced into the Karman's vortex steet flow meter has been arranged to flow along a minimum length flow path between the air introduction port and the inlet port of the Karman's vortex street flow meter. In other words, the sucked air has flowed through the central portion of the air cleaner in a concentrated manner. As a result, only that central portion of the air cleaner has been used to filter the air and has become greatly contaminated and also may oftentimes be deformed by the stream of the sucked air.
Furthermore it has been known to use the Karman's vortex street flow meter as described above to detect the flow rate of a fluid flowing in a pair of different directions through respective conduits. In the latter case the flow rate of the fluid has been detected either by disposing the Karman's vortex street flow meter in each of the conduits or by disposing the Karman's vortex street flow meter in a conduit following a junction where the fluid portions flowing through the respective conduits have joined each other. It is well known that, in order to rectify the measured fluid introduced thereinto, Karman's vortex street flow meters are required to include a conduit on the upstream side thereof having a length equal to at least five times the diameter of the conduit for the same and a conduit on the downstream side thereof having a length equal to about three times that diameter. Thus the use of the Karman's vortex street flow meters as described above has been disadvantageous in that the conduit therefor becomes long.
Accordingly it is an object of the present invention to provide a new and improved Karman's vortex street flow meter including a vortex generating portion having a structure which is inexpensive and simple as compared with the prior art structure.
It is another object of the present invention to provide a new and improved sucked air detector utilizing the Karman's vortex street flow meter as described in the preceding paragraph to detect an amount of air sucked into an internal combustion engine.